1.1 Technical Field
The present invention relates to a process for the polymerization or copolymerization of at least one monomer which can be polymerized or copolymerized by the radical route in the presence of a stable free radical and of an iniferter.
1.2 Description of Related Art
An iniferter is a molecule which generates free radicals by decomposition, wherein the said free radical is able to initiate a polymerization or copolymerization, promote transfer reactions particularly of the said iniferter, and promote termination reactions. An iniferter is characterized by the following reactions involved in polymerization:
formation of free radicals from an iniferter: PA1 initiation and polymerization: EQU A.sup.. +X.fwdarw.AX.sup.., (2) EQU AX.sup.. +X.fwdarw.AXX., . . . , EQU A(X).sub.n-1 X.sup.. +X.fwdarw.A(X).sub.n X.sup.. PA1 transfer reaction involving the said iniferter: EQU A(X).sub.n X.sup.. +AB.fwdarw.A(X).sub.n-1 B+A.sup.. (3) PA1 termination reaction involving a free radical generated from the said iniferter: EQU A(X).sub.n X.sup.. +B.sup...fwdarw.A(X).sub.n+1 B (4) PA1 tetraethylthiuram disulphide, PA1 tetramethylthiuram disulphide, PA1 N,N'-diethyl-N,N'-bis(2-hydroxyethyl)thiuram disulphide, PA1 N,N'-bis(N-(2-phthalimidoethyl)piperazine-thiuram disulphide, PA1 diisopropyl xanthate disulphide. PA1 N-tert-butyl-1-phenyl-2-methylpropyl nitroxide, PA1 N-tert-butyl-1-(2-naphthyl)-2-methylpropyl nitroxide, PA1 N-tert-butyl-1-diethylphosphono-2,2-dimethylpropyl nitroxide, PA1 N-tert-butyl-1-dibenzylphosphono-2,2-dimethylpropyl nitroxide, PA1 N-phenyl-1-diethylphosphono-2,2-dimethylpropyl nitroxide, PA1 N-phenyl-1-diethylphosphono-1-methylethyl nitroxide, PA1 N-(1-phenyl-2-methylpropyl)1-diethyl-phosphono-1-methylethyl nitroxide. PA1 glycidyl, norbornyl, isobornyl (meth)acrylates, 25 methacrylonitrile or mono- and di (C.sub.1 -C.sub.18 alkyl) (meth) acrylamides. PA1 either by breaking the A--X bond of the polymer chain, with a new A--X bond being immediately reformed after insertion of the unit between A. and the new monomer unit, PA1 or by breaking the X--E bond of the polymer chain, with a new X--E bond being immediately reformed after insertion of the unit between E. and the new monomer unit. PA1 in the absence of light, wherein the A--X bond is reversible under the effect of light; and PA1 in the absence or presence of light, wherein the A--X bond is not reversible under the effect of light; and PA1 at the temperature that is sufficient, and not high enough for the spontaneous polymerization or copolymerization of the monomer, without involving the structure A--(X).sub.n --E, to become predominant. PA1 % of conversion: % of monomer converted to polymer. It has been determined by .sup.1 H NMR on a Bruker 200 MHz device with integration of the peaks corresponding to the polymer and to the monomer. PA1 Number-average molecular mass (represented by Mn): Gel permeation chromatography (GPC) in THF at 30.degree. C., after calibration with standard polystyrene samples. PA1 Polydispersity index (represented by Pi): ratio of the weight-average molecular mass to the number-average molecular mass, both measured by GPC (see Mn above).
A-B.fwdarw.A.sup.. +B.sup.. (1)
In reactions (1) to (4), A-B represents an iniferter; X represents a monomer polymerized through the radical route; n is a non-zero integer.
It is accepted by a person skilled in the art that reactions (1) to (4) characterize iniferters. Reactions (3) and (4) result in short chain formation. Therefore, according to the prior art, iniferters have been only useful in the preparation of oligomers.
When an iniferter is used in a polymerization or copolymerization reaction at a temperature where the reaction would take place and proceed to a substantial extent even in the absence of an iniferter or initiator, polymers or copolymers are obtained with broad and bimodal molecular mass distribution comprising mainly two groups of molecules distinct in molecular mass. The presence of the low molecular mass group is caused by the iniferter, and particularly, through reactions (3) and (4). The production of polymers or copolymers with a bimodal molecular mass distribution is not generally desired because of, for example, the interior heterogeneities which affect the mechanical properties of the final material.
In the prior art, for this reason, an iniferter can only be used at a temperature generally less than 100.degree. C., at which no polymerization would take place and proceed to a substantial extent in the absence of iniferter or other polymerization initiators. Accordingly, an iniferter can only be used in the preparation of oligomers, for example, of polymers with an average molecular mass of less than 10,000. An iniferter should therefore not be confused with a conventional polymerization initiator such as azobisisobutyronitrile, benzoyl peroxide, or dicumyl peroxide. Conventional initiators do not generate the reactions (3) and (4), and therefore, do not result in the formation of polymers or copolymers with a bimodal molecular mass distribution, even at a temperature wherein polymerization or copolymerization would take place and proceed to a substantial extent in the absence of any initiators.
Patent Application WO 94/11412 illustrates the action of stable free radicals on the polymerization of styrene. U.S. Pat. No. 5,412,047 illustrates the action of stable free radicals on the polymerization of acrylates. U.S. Pat. No. 5,449,724 illustrates the action of stable free radicals on the polymerization of ethylene. The following references may also be of interest: WO 95/26987, U.S. Pat. No. 4,581,429, EP 507 036, EP 418 118, EP 342 073 or EP 338,918.